1. Field of the Invention
This invention relates to a pilot injection control system and more particularly to a pilot injection control system capable of monitoring the pilot injection state of an injection nozzle and utilizing the monitored state to ensure stable pilot injection.
2. Prior Art Statement
In diesel engines it is a common practice to divide the fuel injection into a pilot injection (initial injection) stage and an ensuing main injection stage so as to reduce ignition delay, prevent generation of oxides of nitrogen and lower combustion noise.
Pilot injection control is difficult, however, because the quantity of fuel injected in each diesel engine cylinder during pilot injection is required to be regulated to an extremely small value on the order of, for example, 5 mm.sup.3 /stroke and, moreover, the injection quantity is highly sensitive to the valve-opening pressure of the fuel injection nozzle.
As taught in Japanese Patent Public Disclosures Sho 63-18156 and Hei 4-175438, for example, it has therefore been proposed to provide means for detecting the presence/absence or the quantity of pilot injection by the fuel injection nozzle and to feedback control the pilot injection based on the result of the detection. However, this method requires every fuel injection nozzle or every cylinder equipped with a fuel injection nozzle to be provided with a sensor for detecting the pilot injection state. It thus results in a complex and expensive control system.
This invention was completed in the light of the foregoing problem and has as its object to provide a pilot injection control system capable of ensuring stable pilot injection with a simple control system.